By "what mindset" I mean how you should be operating this faction. For example, I assume WM is supposed to be played conservatively, requires solid positional play, and is very heavy on support weapons.
Is my WM "idea of operation" correct? And what about the other factions?
Yes your "idea of operation" is largely correct. Its up to you how to play each faction, you only have to change your build order accordingly.
OKW: strong early and late game, infantry heavy
SOV: allrounder, commander choice is essential
UKF: late game, flexible
USF: early-mid game, mobile force